Idiopathic scoliosis (IS) is a structural lateral curvature of the spine present in the late juvenile or adolescent period in otherwise normal individuals. Previous studies from a number of populations have suggested autosomal dominant, X-linked and/or multi-factorial modes of inheritance. As part of a large collaborative study of familial idiopathic scoliosis, 202 families (1198 individuals), each with at least two individuals with scoliosis, have been ascertained and clinically characterized. Phenotypes include degree of lateral curvature, curve type, age of onset and sex. A genome-wide screen was performed at the Center for Inherited Disease Research. The families were ranked based on the ratio of the likelihood of each family given an X-linked model relative to that of an autosomal model. The mode of inheritance for families in the upper tail of the distribution was assumed to be X-linked, while that of the families in the lower tail was assumed to be autosomal dominant. The families were stratified by mode of inheritance and by clinical subtype to reduce genetic heterogeneity and maximize the potential of finding the genes involved in this complex disorder. Evidence has been found for linkage to a region on the X chromosome in a subset of these families.